HMV hydraulic nut mounting: how to fit a tapered bore bearing onto an adapter sleeve

The HMV hydraulic nut is a mounting tool that allows tapered bore bearings to be fitted onto adapter sleeves or directly onto tapered shafts. Unlike a mechanical nut, which is tightened with a wrench, the HMV uses oil pressure to generate a controlled axial thrust. This facilitates the displacement of the bearing along the taper without impacts or excessive heating. In industrial maintenance it is used when space is limited or when precision in the fit is required.

The principle is simple: the nut is screwed onto the threaded end of the sleeve or shaft, and a hand pump injects oil behind an annular piston. That piston pushes against the bearing or against an intermediate washer, moving it axially. Since the bore is tapered, each millimetre of advance reduces the internal clearance of the bearing. That is why mounting with an HMV hydraulic nut is the recommended method for medium and large bearings, where the interference fit is important.

In the SKF catalogue, hydraulic nuts of the HMV series are identified with codes such as HMV 10E or HMV 19E. To choose the correct nut, you need to know the thread of the sleeve or shaft. At MR we supply these nuts and help you select the one that corresponds to your application.

The adapter sleeve is a steel sleeve with a cylindrical bore and a tapered outer surface. It slides onto the shaft and serves as a seat for tapered bore bearings, identified with the K suffix. As the bearing advances on the taper, the sleeve is compressed against the shaft and becomes fixed by interference. Sleeves of the H series, such as H 207 or H 306, are used on transmission shafts, fans and pumps.

Each sleeve has a thread on its larger end to accommodate a lock nut or a hydraulic nut. It also has a slot for the tab of the lock washer. Before mounting, check that the shaft diameter is within the specified tolerance and that the surface is clean and free of burrs. A scratched or rusty shaft can prevent the correct seating of the sleeve.

To choose the correct sleeve, you need the shaft diameter and the bearing code. At MR we distribute SKF adapter sleeves and quote the complete assembly: sleeve, lock nut and hydraulic nut if you need it.

Once the bearing has reached the desired position on the sleeve, it must be fixed axially so that it does not loosen during operation. For this, a KM series lock nut is used, such as KM 9 or KM 5. These nuts have a fine thread and are tightened against the bearing or against a lock washer. Their function is to maintain the preload or internal clearance achieved during fitting.

The KM nut is installed after removing the hydraulic nut. It is screwed on by hand until it bottoms out and then tightened with a hook or impact wrench, depending on size. To prevent it from loosening, a tab of the lock washer is bent into a slot of the nut. It is important not to replace the washer with an ordinary washer, because the tab is what locks the assembly.

When ordering a lock nut, it is advisable to indicate the sleeve code or the thread diameter. At MR we supply SKF lock nuts and help you confirm compatibility with your sleeve.

Before starting, gather all the parts: the tapered bore bearing, the adapter sleeve, the HMV hydraulic nut, the hand pump with pressure gauge and the recommended clean oil. You also need the KM lock nut with its lock washer for the final closure. The shaft must be clean, dry and free of surface damage. It is recommended to measure the shaft diameter at several points to ensure it is within tolerance.

The sleeve is slid onto the shaft to the approximate working position. Then the bearing is placed on the taper, pushing it by hand until it makes contact. The HMV hydraulic nut is screwed onto the threaded end of the sleeve until the piston touches the bearing or an intermediate washer. It is key that the nut is well aligned and that the piston is fully retracted before starting to pump.

A common mistake is not purging the air from the hydraulic circuit. If air remains inside the nut, the advance will be irregular and the pressure gauge will give false readings. Therefore, pump slowly until oil comes out without bubbles from the bleed screw. At MR we quote the HMV hydraulic nut you need.

With the HMV nut in position and the circuit purged, start pumping oil slowly. The piston advances and pushes the bearing onto the sleeve taper. As the bearing moves, the sleeve is compressed against the shaft and the internal clearance of the bearing decreases. The operator must monitor the pressure gauge and, if possible, measure the radial clearance with feeler gauges before, during and after mounting.

The advance must be uniform and without pressure spikes. If the pressure rises sharply without the bearing moving, stop and check: there may be dirt on the taper, lack of lubrication on the thread or a mispositioned sleeve. Never force with impacts or heat the bearing if using a hydraulic nut, because control of the fit is lost. The HMV nut allows cold, clean and repeatable mounting.

The final fitting point is determined by the residual internal clearance or by the clearance reduction specified by the bearing manufacturer. There is no universal pressure: it depends on the bearing size, the fit and the condition of the shaft. Therefore, it is essential to record the mounting pressure and axial displacement for future maintenance. Each nut, such as HMV 10E or HMV 19E, corresponds to a specific thread, so it must match that of the sleeve or shaft.

When the bearing has reached the correct position, release the pressure from the hydraulic nut and unscrew it carefully. In its place, fit the lock washer and the corresponding KM lock nut. The nut is tightened firmly against the bearing or against the washer, depending on the design. Then a tab of the washer is bent into a slot of the nut to prevent it from loosening.

It is important not to reuse old lock washers if the tabs are fatigued or broken. A damaged washer can allow the nut to loosen and the bearing to lose its fit. At MR we supply SKF lock nuts and compatible lock washers, so that the mounting is secure. We also quote the complete assembly: sleeve, hydraulic nut and lock nut.

After fixing the nut, it is recommended to turn the shaft by hand to verify that the bearing rotates smoothly and without hard spots. If irregular resistance is felt, there may be an alignment or dirt problem. In that case, it is advisable to disassemble and check before putting the equipment into operation. A job done well with an HMV hydraulic nut prolongs bearing life and prevents premature failures.

One of the most frequent mistakes is using a hydraulic nut with the wrong thread. If the thread does not match that of the sleeve, both the nut and the sleeve can be damaged. Therefore, check the sleeve code and thread before ordering the HMV. Another mistake is not lubricating the thread and piston before mounting, which increases friction and distorts the pressure indicated by the gauge.

It is also common to confuse the hydraulic nut with the lock nut. The HMV is a mounting tool that is removed after fitting; the KM is the one that remains fixed on the equipment. The HMV should not be left mounted in service, because it is not designed to withstand continuous axial loads. When ordering spare parts, it is advisable to send a photo of the sleeve and bearing, or indicate the codes engraved on the parts.

At MR we work with SKF HMV hydraulic nuts, H adapter sleeves and KM lock nuts. If you have doubts about compatibility, we will indicate the correct combination for your shaft and bearing. You can write to us via WhatsApp or email with the bearing code, shaft diameter and a photo of the assembly. We will quote the parts promptly.